Conventionally, there are devices that enable directional sound pickup by performing directivity synthesis processing of picked-up sound signals from a plurality of microphones. Examples of the devices that enable directional sound pickup include remote conference systems including a sound pickup device, digital video cameras and digital still cameras (DSC).
In such a device capable of directional sound pickup (hereinafter also referred to as “sound pickup device”), an apparatus section that performs directivity synthesis processing (hereinafter referred to as “sound processing apparatus”) utilizes a phase difference between sound waves for the directivity synthesis processing. Thus, the sound processing apparatus requires processing for delaying a picked-up sound signal. The amount of delay used in the delay processing is set based on an inter-terminal sound distance. The inter-terminal sound distance refers to an acoustic distance between two terminals picking up sound (here, microphones; hereinafter referred also to as “sound pickup units”). More specifically, the inter-terminal sound distance refers to a difference between arrival times of sound waves from the terminals multiplied by the speed of sound when a sound source exists on a straight line axis connecting the terminals.
Use of an incorrect delay amount in delay processing may result in a failure to obtain an intended directivity pattern (hereinafter referred to as “directivity characteristic” or “polar pattern” as appropriate). Accordingly, a delay amount needs to be a proper value corresponding to an actual inter-terminal sound distance. Setting a delay amount corresponding to an actual inter-terminal sound distance enables the sound processing apparatus to, for example, at the time of sound pickup, pick up sound from a particular direction, such as a speech voice, with the ambient noise suppressed.
However, the actual inter-terminal sound distance may deviate from an actually-measured distance between the terminals (which is a mechanistic design value) because of the influence of structural objects around the terminals such as a housing in which the microphones are incorporated. In this case, the sound processing apparatus may use an improper delay amount.
Therefore, for example, the technique described in PTL 1 (hereinafter referred to as “related art”) is a technique for setting a proper delay amount.
First, from picked-up sound signals from two microphones for which an inter-terminal sound distance is known among four microphones, the related art estimates a position of a sound source based on the known inter-terminal sound distance. Then, the related art estimates positions of the other microphones from picked-up sound signals from the other microphones based on the estimated position of the sound source. More specifically, the related art adjusts the estimated values of the sound source position and the respective microphone positions so as to reduce a square error between a delay amount between the two microphones for which an inter-terminal sound distance is unknown, and an actually-measured value of such delay amount. This delay amount is calculated from the position of the sound source.
For example, a sound source is disposed at a predetermined position in one direction from among directions on a straight line connecting two microphones of a sound pickup device in an anechoic room (hereinafter referred to as “axial directions”). Then, the aforementioned related art is applied to adjust estimated values of the positions of the microphones so as to minimize the square error. Consequently, a sound processing apparatus to which the related art has been applied can estimate an actual inter-terminal sound distance with good accuracy from an angle of a direction of a sound source and a delay amount in directivity synthesis processing to provide an arbitrary directivity pattern with good accuracy.